The present invention is concerned with adhesively bonding a die to an organic chip carrier, and is especially concerned with significantly reducing, if not entirely eliminating, the problem of adhesive bleed-out. The present invention is concerned with adhesively bonding a die to an organic chip carrier along with assuring that the metallic surface on the chip carrier remains wire bondable. The present invention provides for reducing die attach adhesive separation and thereby reducing contamination and/or staining of substrate surfaces due to the adhesive. The present invention also relates to adhesive compositions that exhibit reduced bleed-out.
Packaging techniques for integrated circuits have been developed with an emphasis on miniaturization. Improved methods enable integrating millions of transistor circuit elements into single integrated semiconductor embodied circuits or chips, and has resulted in increased emphasis on methods to package these circuits in space efficient, yet reliable and mass producible packages.
Forming an electronic system requires combining a plurality of integrated circuits and electrically connecting integrated circuits together. Once connected, other devices such as keyboards, video monitors and printers may be connected to and utilized with the electronic system.
In order to accomplish this interconnection, conductive paths must be made available to connect the internal circuitry of the integrated circuit die to external system electrical circuits. The integrated circuit die uses metallized bumps or xe2x80x9cbond padsxe2x80x9d which are connected to the integrated circuits of the die.
The integrated circuit package contains conductors referred to as xe2x80x9cbond fingersxe2x80x9d that are interconnected to the bond pads of the integrated circuit die by wire bonding, tape automated bonding (xe2x80x9cTABxe2x80x9d), wedge bonding, ball bonding or other known methods. The bond fingers are connected to the integrated circuit package pins that are used to connect to printed circuit boards or cards.
Before the integrated circuit die bond pads are connected to the integrated circuit package, the die must be attached to the package assembly. Organic adhesives, such as, for example an epoxy-based adhesive, an acrylic-based adhesive or a silicone has been used for attachment of the die to the package assembly. Typical epoxy adhesives also include silver filler particles for protecting against sparking.
Although the adhesives used are relatively viscous, they nevertheless have a propensity to bleed and spread out away from the point of attachment. For example, the adhesive has a tendency to bleed-out along the periphery of the die attachment area and spread out over adjacent areas such as bond finger areas where electrical connections ultimately need to be made.
Various methods for reducing resin bleed have been developed. For example, the chip carrier surface may have a recess at the point of attachment of the die, such that the die and adhesive will be recessed below the adjoining areas of the chip carrier where electrical bonding sites are located. As a drawback to this method, not all integrated circuit assemblies provide the option of a recess cavity in the carrier surface. Very large scale integrated circuit (VLSI) assemblies, for example, require a large number of bonding sites and these are at the same level as the die attachment surface.
U.S. Pat. No. 5,409,863 suggests a method for controlling adhesive spread during a die-attach process. This method incorporates a low profile barrier, such as a solder mask ring, into the chip carrier structure. The barrier surrounds the periphery of the die attachment area, preventing the spread of adhesive resin onto the adjacent bonding sites on the chip carrier.
Also, attempts to deal with this problem have included plasma cleaning after the-die attachment. However, such technique has not been especially effective in eliminating bleed-out of the adhesive. It has also been suggested to treat surfaces with fluorinated coupling agents or other types of surfactants in order to render the surfaces non-wettable to the adhesive resin. However, these processes must be carefully controlled and are extremely time consuming and relative expensive. Furthermore, the shelf life of surfaces treated in such manner is typically rather limited, from hours to a few days, further restricting their use.
It would therefore be desirable to provide a technique for preventing adhesive spreading of die attachment onto adjacent bond fingers when fabricating semiconductor integrated circuit dies along with the integrated circuit package.
The present invention provides for reducing contamination and/or staining of substrate surfaces by the bonding adhesive. Moreover, the present invention provides a process that does not significantly increase the time and/or expense of the die attach process.
According to the present invention, an organic chip carrier having metallic circuitry and wire bond pads thereon is bonded to an underlying die by a photocurable adhesive and electrically interconnected together with wire bonding to the wire bond pads.
In addition, the present invention is also concerned with a method of fabricating a semiconductor integrated package whereby the integrated circuit adhesive does not spread out onto bond finger connections of the package. The method of the present invention comprises providing an adhesive on bond areas of an integrated circuit chip carrier. The adhesive is a photocurable adhesive composition. The composition is exposed to actinic radiation in order to render the adhesive bleed-free. The integrated circuit die is placed over the adhesive pattern so as to produce an adhesive fillet along the die edge. The adhesive can be subjected to the actinic radiation prior to or after the die placement since the exposure to actinic radiation imparts cross-linking to the composition thereby preventing spreading of the resin but does not fully harden the adhesive and thereby permitting it to retain sufficient adhesive strength to create a bond between the die and even if attached after subjecting to the actinic radiation.
After the die is assembled with the organic chip carrier and the exposure to actinic radiation is carried out, the assembly is subjected to a post-bake at elevated temperatures in order to fully cure and harden the adhesive and create the necessary adhesive bond between the organic chip carrier and integrated circuit die.
The present invention also relates to compositions suitable for use in the above-described process. Compositions of the present invention exhibit dual curing characteristics along with stable shelf-life. Moreover, the compositions are photocurable and are rendered free from resin bleed upon curing with actinic radiation. More particularly, the compositions comprise:
A. An epoxy component that includes at least one polyepoxide resin curable by heat;
B. An olefinically unsaturated monomer component that includes at least one polyolefinically unsaturated monomer curable by actinic radiation;
C. At least one cyanate ester;
D. At least one photoinitiator;
E. At least one organic peroxide; and
F. At least one heat activated curing agent selected from the group consisting of organo-metallic compounds, inorganic metal salts, phenolic compounds; solutions of organo-metallic compounds in phenolic compounds; and mixtures thereof.
Still other objects and advantages of the present invention will become readily apparent by those skilled in the art from the following detailed description, wherein it is shown and described only the preferred embodiments of the invention, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, without departing from the invention. Accordingly, the description is to be regarded as illustrative in nature and not as restrictive.